Dr. DA Henderson, the man who eradicated smallpox from this planet, has died. There are no words that can do adequate justice to this benefactor of humankind whose genius and ingenuity will be known for millennia. I write as one of the extremely fortunate individuals who can call DA not just hero but mentor.

I first met DA about 8 years ago as an infectious disease fellow. I can still recall my sheepish uttering of "Dr. Henderson" when I met him in his office as he sat amongst innumerable awards commemorating the incalculable debt humankind will owe him in perpetuity. DA, despite my naivety, thoroughly embraced me in a way reminiscent of the manner of a grandfather -- if your grandfather was a man who slayed dragons for a living. I am sure I am not unique in this feeling about DA as there are scores of his mentees worldwide who likely have similar sentiments.

DA was a force. He was someone who would never, ever, balk from calling a spade a spade. However cliched the phrase "speaking truth to power" may be, DA exemplified it. One of my first glimpses of this unrivalled ability of his was during the 2009 influenza epidemic where, just upon hearing preliminary information regarding its trajectory, he had its number. Incidentally, during that pandemic he and I coauthored a piece inspired by his recollection of the concept of antigenic sin---which I believe will be the highlight of my career. During this pandemic, DA was wont to add insightful suggestions as well as pointed criticism when warranted.

During Ebola in 2014, again DA showed his prowess arguing that directing control measures against those who were most contagious made the most sense in quelling the outbreak (another paper I was lucky enough to coauthor with him).

Time and again, DA was proven right and his insight steered infectious disease medicine in a unique manner in which no one else could.

In DA's last days, another of my mentors--Dr. Tom Inglesby--called me and told me to visit with DA as he really wanted to talk about infectious disease. I am eternally grateful to Tom for that call as my last visit with DA is something that I will never forget. What did we talk about? Here are two statements of DA made during our last discussion:

"What virus do you want to talk about next?"

"What other puzzles are there?"

These two statements from DA exemplify all that I want to be in my life-- someone so passionate and dedicated to productive work in my field that nothing refrains me from engaging in discussion about it, despite any circumstances I find myself in. The devotion DA had to his work, his ideas, and his mind is something unfortunately all too rare in the world today.

There are many recollections I have of working in the same office as him. Gone are the days when I can walk down to his office and hear him dissect the latest outbreak offering glimmering pearls as to what he determined to be the trajectory and implications of this latest insult on the human species -- something that continued up to and including Zika. But this impact is even more profound as the entire world counted on DA's wisdom to set the course of its battles against myriad infectious diseases from polio to guinea worm.

I heard that DA's health took a final turn for the worse as I was about to give a lecture on biosecurity, a field he was basically the founder of and who conceived of and founded the center of which I am a member. His leadership during the anthrax attacks of 2001 made the nation, and the world, safer and more prepared for bioterrorism than it ever had been. The ripple effects of his leadership will echo for decades. As I spoke, I suppressed emotions I had about a man who indelibly affected me and whom I knew I could never repay.

If there were a Valhalla, I would like to imagine Pasteur, Koch, Lister, Salk, Sabin, Theiler, Ross, Semmelweis, Jenner, DA's mentor Alex Langmuir and the pantheon of the infectious disease luminaries, to whom the human race owes so much, on their feet, clapping in unison to welcome the man who took their ideas to their logical conclusion and rid mankind of an infectious scourge rendering it incapable of harming a human again.

I will never forget all that DA taught me and will always try to live up to the example he set. I will never cease regaling people with the stories of his life and achievements as they serve as an inspiration for what one human can aspire to be.

What would DA do (WWDAD)? If that were to become the reigning paradigm in our field, I would surmise the human race would do just fine.